As the prevalence of consumer electronics (e.g., mobile phones, tablets, and laptop computers) and electrified-vehicle (i.e., EV) automobiles (e.g., plug-in hybrids and BEVs) has increased, so too has the demand for better performing energy storage devices which are required to power these consumer electronics and vehicles. While rechargeable lithium (Li) ion batteries are popular energy storage devices for consumer electronics, currently available rechargeable lithium (Li) ion batteries are still too limited with respect to their energy density and power output for mainstream consumer adoption in automotive as well as other energy-intensive application. In order to improve upon the energy density and power output of rechargeable Li batteries, Li-metal has been proposed as a next-generation negative electrode material since such electrodes theoretically produce the highest energy densities possible by minimizing a battery's discharged voltage (i.e., V of Li in Li-metal is 0V) and maximizing the charged voltage [See, e.g., Andre, Dave, et al., J. Mater. Chem. A, DOI: 10.1039/c5ta00361j, (2015)]. By pairing a Li-metal negative electrode with a highly ion-conducting solid state electrolyte, the stored energy in a highly energy-dense rechargeable Li ion batteries should theoretically be accessed at commercially viable power rates.
When a Li-rechargeable battery discharges, Li+ ions conduct through an electrolyte from a negative to a positive electrode and vice versa during charge. This process produces electrical energy (Energy=Voltage×Current) in a circuit connecting the electrodes and that is electrically insulated from, but parallel to, the Li+ conduction path; the Voltage (V versus Li) being a function of the chemical potential difference for Li situated in the positive electrode as compared to the negative electrode. In order to use Li-metal negative electrodes, however, new solid state electrolytes are required as the known and widely used liquid electrolytes are chemically incompatible with Li-metal.
Solid state Li-rechargeable batteries which include solid state electrolytes are an attractive alternative to conventional Li-rechargeable batteries, in part due to the aforementioned higher energy densities (e.g., gravimetric or volumetric) and power rates but also due to their safety attributes which are related to the absence of an flammable organic liquid electrolyte. Although Li-metal negative electrodes maximize a battery's energy density, Li-metal is unfortunately highly reactive with most electrolytes and has a large volume change (e.g., contraction and expansion) when discharged and charged. This volume change mechanically strains, and can crack, a solid state electrolyte which contacts the Li-metal. This mechanical stability issue is worsened if the electrolyte also chemically reacts with Li-metal. To date, there are no viable commercially available solutions to either of these chemical or mechanical stability problems, nor are there solutions to other problems such as resistance/impedance gain, which are associated with interfacing Li-metal negative electrodes with solid state electrolytes.
Some solid state electrolytes have been analyzed, such as oxide- or sulfide-based electrolytes. See, for example, U.S. Pat. Nos. 8,658,317, 8,092,941, 7,901,658, 6,277,524 and 8,697,292; U.S. Patent Application Publication Nos. 2013/0085055 (issued as U.S. Pat. No. 8,940,220 on Jan. 27, 2015), 2011/0281175 (issued as U.S. Pat. No. 9,017,882 on Apr. 28, 2015), 2014/0093785 (abandoned), 2014/0170504 (abandoned), 2014/0065513issued as U.S. Pat. No. 9,502,729 on Nov. 22, 2016), and 2010/0047696 (issued as U.S. Pat. No. 8,883,357 on Nov. 11, 2014); also Bonderer, et al. Journal of the American Ceramic Society, 2010, 93(11):3624-3631; Murugan, et al., Angew Chem. Int. Ed. 2007, 46, 7778-7781; Buschmann, et al., Phys. Chem. Chem. Phys., 2011, 13, 19378-19392; Buschmann, et al., Journal of Power Sources 206 (2012) 236-244; Kotobuki, et al., Journal of Power Sources 196 (2011) 7750-7754; and Jin, et al., Journal of Power Sources 196 (2011) 8683-8687. Some composites of these electrolytes are also known. See, for example, Skaarup, Steen, et al., Solid State Ionics 28-30 (1988) 975-978; Skaarup, Steen, et al., Solid State Ionics 40/41 (1990) 1021-1024; Nairn, K., et al., Solid State Ionics 86-88 (1996) 589-593; Nairn, K., et al., Solid State Ionics 121 (1999) 115-119; Kumar, Binod, et al., Journal of Electroceramics, 5:2, 127-139, 2000; Wang, Yan-Jie, et al., Journal of Applied Polymer Science, Vol. 102, 1328-1334 (2006); Thokchom, J. S., et al., J. Am Ceram. Soc., 90 [2] 462-466 (2007); Wieczorek, W. et al., Electronic Materials: Science and Technology Volume 10, 2008, pp 1-7; Li, Qin, et al, Solid State Ionic 268 (2014) 156-161; Aetukuri, N. B., et al., Adv. Energy Mater., 2015, pages 1-6; Lim, Y. J., et al., ChemPlusChem, DOI: 10.1002/cplu.201500106; Liu, W., et al., DOI: 10.1021/acs.nanolett.5b00600; and Nam, Y. J., et al., Nano Lett., 2015, 15 (5), pp 3317-3323), Despite their ability to conduct Li+ions, these solid electrolytes have yet to demonstrate sufficiently high ion conductivity, sufficiently long cycle-ability, a high coulombic efficiency at high cumulative Li throughput, the ability to prevent the formation of lithium dendrites, or the ability to be formulated or prepared with the proper morphology (e.g., thin, flexible film) or sufficient particle connectivity (i.e., particle-particle necking) to function as required for commercial applications.
Conventional Li-rechargeable batteries uses a liquid electrolyte and a thin polymer membrane disposed between two electrodes. The polymer membrane is sometimes referred to as a separator. The polymer membrane is used primarily to prevent direct contact between the two electrodes. Small holes in the polymer membrane allow the liquid electrolyte to flow between the two electrodes for ionic conductivity. Formation of lithium dendrites can be slowed, though not prevented, by minimizing nucleation points available for the dendrites to grow from, e.g., by using smooth electrodes formed by passing these electrodes through a roll press. When dendrites start growing in such a cell, the polymer membrane is not robust enough to prevent these growing dendrites from piercing through the membrane and eventually causing the internal short between the two electrodes. What is needed, in the relevant field, then is a robust electrolyte system which may be capable of blocking dendrites from piercing through the system. What is needed, in the relevant field, is, for example, an electrolyte system which can act as a mechanical barrier to prevent the growth of dendrites in the direction between two electrodes. If a solid electrolyte is combined with one or more polymers, the mechanical properties of this combination may provide operable electrolyte characteristics (e.g., ionic conductivity, electrical resistance) and mechanical characteristics (e.g., yield strength, yield strain, ultimate strength, and ultimate strain) that are capable of withstanding dendrite growth and preventing dendrites from piercing through the composite electrolyte. The minimum mechanical characteristics needed to block lithium dendrites may depend on localized voltage values, interface geometry, and other characteristics. Furthermore, small variations in composition of composite electrolytes may yield substantial changes in these mechanical characteristics.
There is therefore a series of problems in the relevant field related to solid state electrolytes which are chemically and mechanically compatible with Li-metal electrodes, are robust, and have sufficient ionic conductivity for commercial battery applications. What is needed in the relevant field is, for example, chemically and mechanically stable thin film solid state electrolytes with sufficient conductivity for energy dense rechargeable batteries and which accommodate Li-metal's volume expansion and contraction during battery charge and discharge. The instant disclosure sets forth electrolytes, for example, composite electrolytes, in addition to methods for making and using these electrolytes and composite electrolytes. The instant disclosure sets forth other solutions to problems in the relevant field.